Switch-mode bi-directional thermoelectric control of laser diode temperature

ABSTRACT

A system for actively heating and cooling an object contains a thermoelectric device having a Peltier junction. The system is capable of reversing the direction of DC current flow through the Peltier junction so that the thermoelectric cooler/heater either heats or cools the object, as selected. The DC power supply is preferably operated in switch-mode. The thermoelectric device is disposed in a laser diode module or in heat-conductive contact with a laser housing mounting plate in a high-density laser source bank.

RELATED APPLICATIONS

[0001] This application claims benefit of priority to provisional application serial No. 60/272,997 filed Mar. 2, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to methods, systems and structures for thermoelectric temperature control, in particular, to thermoelectric control of laser diodes and other opto-electronic devices.

[0004] 2. Statement of the Problem

[0005] In many applications, active temperature control improves the performance of opto-electronic devices. For example, laser diodes are useful in many fields of technology. They are small and efficient. They can be directly modulated and tuned. These devices affect us daily with better clarity in telephone systems, high fidelity in music, and in many less obvious ways. An important electrical characteristic of a laser diode is the relation of light power to laser current, often represented by light-current curves in graphs in which output light intensity is plotted as a function of drive current. These curves are used to determine a laser's operating point (drive current at the rated optical power) and threshold current (current at which lasing begins). Light intensity-current curves are strongly dependent on a laser's temperature. Typically, laser threshold current increases with temperature. Emission wavelength is strongly dependent on device temperature. The efficiency of a laser diode is also measured from light-current curves. The efficiency of the diode decreases with increasing temperature. Also, the operating lifetime of a laser diode decreases with increasing temperature.

[0006] In most solid-state detectors, noise decreases with increasing temperature. Responsiveness also varies with operating temperature and, therefore, must be stabilized by active temperature control if a high degree of radiometric accuracy is required.

[0007] Thus, in these and in many other applications, active temperature control can improve the performance of opto-electronic devices. It is known in the art to use thermoelectric “Peltier” devices to cool high-sensitivity transducers and opto-electronic devices, such as charge coupled devices (“CCDs”) and laser diodes, in an effort to improve their performance. As technical instrumentation becomes denser, temperature control becomes both more important and more difficult. For example, it would be more efficient economically and space-wise to combine many laser source modules in a photonic test instrument. A high concentration or density of hot laser sources and associated circuitry, however, makes it more difficult to regulate cooling and to maintain a desired uniform temperature. The use of dedicated Peltier cooling devices does not overcome all of the problems that are presented by increasing densification; for example, the photonic test system may need to stabilize at an operating temperature before test measurements may be performed, or the ambient temperature may be such that cooling alone is unable to stabilize the system temperature within a preferred operating range.

SOLUTION

[0008] The present invention helps to solve some of the problems mentioned above by providing systems and methods for both actively heating and actively cooling an object to obtain accurate and precise control of temperature.

[0009] A basic embodiment, for example, comprises a system for heating and cooling an object that incorporates a first thermoelectric cooler/heater having a Peltier junction between a first contact and a second contact. A switch-mode power supply is electrically connected to the first contact and the second contact, for flowing electrical current through the Peltier junction. A polarity controller controls the direction of electrical current flow through the Peltier junction to provide selective heating and cooling. The basic embodiment is particularly useful in complex electro-optical test measurement systems, such as modular laser diode cards that may be incorporated within high-density optical source banks for use in testing electro-optical systems.

[0010] A significant advantage is obtained in these systems by using the switch-mode power supply because these power supplies operate at much higher efficiencies in these applications than do, for example, linear or non-switch-mode power supplies. A filter, such as a capacitive filter, may be used to smooth the pulsed output from the switch-mode power supply, in order to provide an essentially non-pulsed power source while maintaining the efficiency benefit of pulsed power from the switch-mode power supply. By way of example, a system having an efficiency of approximately ten percent in usage of power from a linear power supply might be upgraded to an efficiency of sixty or seventy percent through the use of a switch-mode power supply. Additional efficiencies are obtained by using a single Peltier junction for both heating and cooling purposes by selectively altering the direction of current flowing through the Peltier junction.

[0011] The control circuitry may comprise various instrumentalities to accomplish switching of the switch-mode power supply for the purpose of maintaining the system temperature within a predetermined temperature range. For example, a polarity controller may be provided for selectively controlling the direction of electrical current flow through the Peltier junction in the first and second directions. A temperature sensor, e.g., a thermistor, may be configured to provide the polarity controller with an input signal that is useful for controlling the system temperature. An error amplifier may be used to provide an output signal by comparing the thermistor signal against a reference voltage representing a desired control temperature. An digital-to-analog converter may be used to provide the reference voltage. A thermal process controller, such as a proportional integral (PI) or proportional integral derivative (PID) controller, can integrate output from the error amplifier to provide control signals based upon the integrated value of the error amplifier output. A polarity controller may accept signals from the thermal process controller for purposes of switching the direction of current from the power supply. The actual switching operation may be performed, for example, through the use of an H-bridge under the command of the polarity controller.

[0012] The circuit components that are described above may be deployed in a series of loops that together form a closed loop feedback system for self-regulation of temperature and power output. For example, the thermistor, the error amplifier, the thermal process controller, the polarity controller and the polarity control bridge may be combined to form a first loop. The switch-mode DC power supply may be connected to the polarity control bridge for supply of power thereto, and an absolute value circuit may optionally be positioned to receive control signals from the thermal process controller. The absolute value circuit may be used to adapt the process control signals, as needed, for submission to the switch-mode power supply, whereby a second loop is formed including the absolute value circuit and the power supply. A third loop or feedback loop may be provided to measure the power output of the switch-mode power supply at the thermoelectric device and adjust the output based upon a comparison to a signal representing a desired power output.

[0013] The concepts that have been discussed above may be utilized to provide a two-stage thermoelectric system that, for example, may be used to control the temperature of a laser diode. One example of a system of this type may include a laser housing containing a laser diode device, and a first switch-mode bi-directional thermoelectric device that is disposed in the laser housing and heat-conductively connected to the laser diode device. This system may further include a heat-conducting mount, such as a block or plate, on which the laser housing is mounted, and a second switch-mode bi-directional thermoelectric cooler/heater that resides on the mount. Thus, the two stage system may heat or cool by virtue of a direct contact with the laser diode package, as well as through contact with the mounting system for the laser diode package. The respective switch-mode bi-directional thermoelectric cooler/heaters may be maintained at different temperatures. These concepts are particularly useful when a plurality of laser diode packages are mounted in a high-density photonic test array.

[0014] The instrumentalities that have been described above may be used in a method of stabilizing temperature in a system having a Peltier junction thermoelectric cooler/heater. The basic method includes the steps of sensing the temperature in the system to provide a temperature signal corresponding to the temperature, and selectively activating the Peltier junction thermoelectric cooler/heater to maintain the temperature within a predetermined temperature range based upon the temperature signal. The sensed temperature may, for example, be that of a laser diode or a mount therefor. The laser diode can be energized to perform optical telecommunications test operations concomitantly with the steps of sensing temperature and selectively activating the Peltier junction thermoelectric cooler/heater for heating or cooling purposes. The heat pump and the heat generator may be selectively activated by the control circuitry through use of the switch mode power supply.

[0015] Additional objects and advantages will be apparent to those skilled in the art upon reading the following detailed description in association with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] A more complete understanding of the invention may be obtained by reference to the drawings, in which:

[0017]FIG. 1 depicts a switch-mode bi-directional thermoelectric control system for heating and cooling an object through use of a bi-directional switch mode thermoelectric cooler;

[0018]FIG. 2 shows a block diagram of switch-mode bi-directional thermoelectric control system for controlling temperature of a laser diode in a laser-diode source bank of a photonic tester;

[0019]FIG. 3 shows a block diagram of a high-density optical source bank in which an embodiment of a bi-directional switch mode thermoelectric cooler is utilized;

[0020]FIG. 4 depicts a cross-sectional view of an exemplary, general-purpose laser diode-mounting fixture in which the relative locations and dimensions of bi-directional switch mode thermoelectric device are shown;

[0021]FIG. 5 depicts a top view of the laser diode-mounting fixture shown in FIG. 4;

[0022]FIG. 6 depicts a laser-diode-mounting fixture in which a laser diode package is mounted on an aluminum block;

[0023]FIG. 7 provides additional detail with respect to the laser diode package shown in FIG. 6;

[0024]FIG. 8 depicts a capacitive filter for use in smoothing the output of the switch-mode power supply; and

[0025]FIG. 9 depicts a power output curve from a switch mode or pulsed DC power supply that has been smoothed over time by action of the circuit shown in FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] A system in accordance with preferred embodiments of the invention provides a solid-state bi-directional thermoelectric device that provides both active heating and active cooling of circuitry that requires operational temperature control by mechanisms beyond normal convectance, in order to perform within specifications.

[0027] A basic embodiment, for example, comprises a system for heating and cooling an object that incorporates a first thermoelectric cooler/heater having a Peltier junction between a first contact and a second contact. A switch-mode power supply is electrically connected to the first contact and the second contact, for flowing electrical current through the Peltier junction. A polarity controller controls the direction of electrical current flow through the Peltier junction to provide selective heating and cooling.

[0028] The preferred use of a switch mode power supply, especially one that is capable of pulse modulating DC current, provides a significant advantage in the cooling heating and system. This advantage exists because the same amount of heating or cooling effect may be obtained with less power dissipation into heat. For example, measurements on test systems have shown that the switch mode power supply may dissipate 10% of its power into heart, whereas a non-switching DC supply dissipates from 60% to 70% of its power. The reduced amount of power dissipation permits, for example, a greater density of laser channel sources to be used in proximity to one another in optical test systems and other applications where heat dissipation is a limiting design factor that limits the amount of densification that may be attained.

[0029] A thermoelectric device in accordance with these principles is useful in a large number of various types of applications, especially in high performance or tight tolerance electrical testing equipment. Various types of temperature sensors may be used to measure the temperature of the object being heated or cooled. The DC electrical current is provided in various ways, preferably by a switch-mode DC power supply. Control of the direction of flow of the DC electrical current through the Peltier junction is effected using any of a large number of different solid-state and analog control systems. The invention is described herein in relation to its use for controlling the temperature of laser diodes in a high-density laser source bank. It is understood, however, that the invention is useful in a large number of technical applications in which temperature, heating and cooling must be accurately and precisely controlled. Therefore, although the invention is described herein with reference to FIGS. 1-7, it is understood that the embodiments described herein are not intended to limit the scope of the invention, which is defined in the claims below.

[0030] A “switch mode” DC power supply is one that permits selective modulation of the DC current, e.g., as a series of positive or negative pulses such as consist of the positive amplitude of a sine wave or an analogous square wave. This pulsing capability significantly reduces Thomson effect heating, which cannot be entirely avoided in a Peltier device. It is not necessary to provide pulse-mode power to directly to the Peltier junction. In fact, it is preferred to filter the pulse-mode output and thereby provide a smoothed power output by averaging the total power to fill in the gaps between pulse spikes. This concept of filtering-to-average- obtains the efficiency benefit of pulsed-mode (i.e., switch-mode) supply while providing optimum power delivery to the Peltier junction thermoelectric cooler/heater in the form of a relatively steady-state current.

[0031] The term “Peltier junction thermoelectric cooler/heater” is used generally in the specification to include both electrical conductors and semiconductors. Any two dissimilar types of material in contact with one another may be used to form the Peltier junction. These materials especially include dissimilar electrically conductive metals. It is well known, however, that two dissimilar semiconductors, for example, n-type and p-type materials, may also be utilized to provide a Peltier effect in thermoelectric cooler/heaters. A particularly preferred Peltier junction thermoelectric cooler/heater comprises n and p-doped silicon.

[0032] The term “bi-directional” is used in the specification to denote that the direction of flow of DC current through the Peltier junction of a thermoelectric cooler/heater in accordance with the invention is selectively controllable and reversible. As a result, a thermoelectric cooler/heater may be used either to heat or to cool. The combination of a switch-mode DC power supplied and the capability to select and reverse the direction of current flow through the Peltier junction is obtained through novel circuitry, as described below.

[0033]FIG. 1 depicts a system 100 for heating and cooling an object 102, such as a laser diode, in accordance with one aspect of the invention. System 100 includes a thermoelectric device 104 comprising a first electrical junction contact 106 and a second electrical junction contact 108 in contact with each other, thereby forming a Peltier junction 110 between first electrical junction contact 106 and second electrical junction contact 108. System 100 further comprises a switch-mode DC power supply 112 and a polarity controller 114 for controlling the direction of electrical current flow through Peltier junction 110. DC power supply 112 is electrically connected to first junction contact 106 and to second junction contact 108 so that it may provide pulse-modulated DC current through Peltier junction 110.

[0034] The polarity controller 114 may have various types of structures and operating techniques to accomplish the function of selectively reversing current flow through Peltier junction 110. Preferably, thermoelectric device 104 includes a heat sink 116 having a large total heat capacity relative to the heating and cooling requirements of object 102. The heat sink 116 may be made of identical material with respect to the second junction contact 108, or it may be a separate component heat-conductively connected by connector 117, as depicted in FIG. 1. A feature of a system in accordance with the invention is that the direction of flow through thermoelectric cooler/heater 104 and through Peltier junction 110 can be changed to effect heating or cooling. In FIG. 1, the flow of current indicated by the arrows of electrical lines 120, 122 is from first junction 106 to second junction 108. In this configuration, heat flows from first junction 106 to second junction 108 into heat sink 116, thereby cooling object 102. In accordance with the invention, the direction of current flow is reversible, so that heat flows from second junction 108 to first junction 106, thereby heating object 102.

[0035] There will now be shown a system in accordance with other aspects that demonstrate, by way of example, additional detail with respect to control circuitry for use in governing the operation of the Peltier thermoelectric device and control the temperature of an object. A switch-mode power supply is electrically connected to the thermoelectric device for flowing electrical current through the thermoelectric cooler/heater through the Peltier junction. A thermistor may be used to convert a temperature of the object to a thermistor voltage. An error amplifier may be used to compare the thermistor voltage to a reference voltage and produce a corresponding error voltage. A PID controller may be used to process the error voltage and produce a corresponding PID signal. An absolute value circuit may be used to convert the PID signal to a negative feedback value for input to the switch-mode power supply. An H-bridge may be used to reverse the direction of current through the Peltier junction. A polarity controller may be used to sense the polarity of the PID signal and control the H-bridge. A current-voltage amplifier may be used to convert the electrical current that flows through the thermoelectric device into a feedback signal for use in controlling the output of the switch mode power supply.

[0036]FIG. 2 shows a block diagram of bi-directional switch-mode thermoelectric control system 200 in accordance with the invention for controlling temperature of a laser diode in a laser-diode source bank of a photonic tester. System 200 includes a thermistor and associated circuitry 202, such as bridge circuitry, for converting a temperature of an object 204 to a thermistor voltage. Object 204 is, for example, a laser diode, another light source such as a light emitting diode, or a mounting block on which a laser diode housing is mounted. Typically, a thermistor having a nominal resistance of 10 K ohms is used in the thermistor and associated circuitry 202. Suitable thermistors are commercially available. For example, a Dale 1T1002-5 is one such thermistor. An error amplifier 206 compares the thermistor voltage to a reference voltage corresponding to a desired reference temperature. Suitable error amplifiers are commercially available, for example, from Analog Devices, model AD706. The reference voltage is created with a digital-to-analog converter, for example, a 12-bit Linear Tech LTC8043 or a 16-bit LTC1595. The difference between the thermistor voltage and the reference voltage is an error voltage. This difference is provided as the output of error amplifier 206 and the input of a thermal process controller 208. Preferably, thermal process controller 208 is a PID controller, for example, a controller from Analog Devices, model ADS706. The controller 208 may also be a proportional-integral controller.

[0037] Additional system components can be added to the control system 200 to accommodate recognized needs. For example, it may be the case that a power supply requires a negative control voltage input to regulate the power output. In this case, an optional absolute value circuit 210 converts the output of thermal process controller 208 so that it is always negative because the switch-mode DC power supply, described below, requires negative feedback regardless of whether the thermoelectric device 216 is heating or cooling. Absolute value circuit 210 is commercially available, for example, from Analog Devices, model AD706. Voltage output from the polarity controller 208 also flows along electrical path 211 to polarity controller 212, which is a voltage comparator for determining whether the voltage is positive or negative corresponding to a temperature above or below the reference temperature. Polarity controller 212 controls an H-bridge 214 in a way that changes the direction of current through the thermoelectric device 216. Suitable comparators are commercially available for use as polarity controller 212; for example, Linear Tech LT1017CS8. H-bridge 214 is a set of transistors used to change the direction of current flowing to thermoelectric device 216. A suitable, commercially available H-bridge is a Fairchild FDS6990 utilizing MOSFETs.

[0038] The output of absolute value circuit 210, that is, a negative feedback voltage value, is transmitted along electrical lines 218 to switch-mode (pulse-modulated) power supply 220. Switch-mode power supply 220 converts the low power negative feedback voltage into DC current at a higher power level. In the preferred embodiment, the output current in electrical line 221 has a value in a range of from about 0 to 1.3 amps, with a corresponding voltage in a range of from about 0 to 13 volts. H-bridge 214 controls the direction of the current flow through the Peltier junction of thermoelectric cooler/heater 216. Depending on the direction of current flow through the Peltier junction at any given time during operation, thermoelectric cooler/heater 216 functions as a heater or a cooler. Numerous types of thermoelectric cooler/heaters suitable for use in accordance with the invention are commercially available. A laser diode module typically includes a laser housing containing a laser diode and a thermoelectric temperature controller. An example of a commercially available laser module is the Lucent D2525P. A commercially available thermoelectric cooler/heater 216 suitable for controlling the temperature of a mounting block (on which a laser module is disposed) is a Melcor CP1.0-63-05L.

[0039] System 200 also includes I-V amplifier 224 that converts the current which flows through the Peltier junction in thermoelectric cooler/heater 216 into a voltage that is used in a minor control loop by being transmitted back through electrical line 225 to power supply 220. The output of I-V amplifier 224 and the output of absolute value circuit 210 are compared. If the outputs are not the same, then the output of power supply 220 is corrected.

[0040] The circuitry represented in FIG. 2 provides efficiency and good control of a switch-mode bi-directional thermoelectric cooler/heater in accordance with the invention. It is understood that analog or digital circuits using different devices in a different order may be used to accomplish the same function without departing from the scope of invention.

[0041] There will now be shown a thermoelectrically controlled high-density laser source bank, comprising a plurality of laser diode source modules, each laser diode source module containing a laser diode and a switch-mode bi-directional thermoelectric cooler/heater having a Peltier junction. The laser source bank may further include a laser housing containing a laser diode device, a first switch-mode bi-directional thermoelectric cooler/heater disposed in the laser housing and heat-conductively connected to the laser diode device, a heat-conducting mounting block on which the laser housing is mounted, and a second switch-mode bi-directional thermoelectric cooler/heater mounted on the mounting block.

[0042] In the prior art, adequate control of laser diode temperature was one of the hindrances against assembling and operating laser source banks having large numbers of laser sources, and has prevented the accumulation of high density source banks having more than about eight to seventeen channels in a single box. The active heating and cooling provided by switch-mode bi-directional thermoelectric cooler/heaters in accordance with the invention contribute to the feasibility of building and operating high-density laser diode source banks.

[0043]FIG. 3 is a block diagram of an optical test system 300 illustrating, by way of example, a modular structure that operates according to preferred principles of the invention. An optical source array 302 is comprised of a plurality of individual channels, such as channel 303, which each contain a corresponding plurality of elements. The optical source array 302 contains a total of N such channels, where N may be, for example, 100 or 200 channels as needed for test purposes. The optical source array 302, as depicted in FIG. 3, consumes less power and occupies a smaller footprint than prior devices. An additional advantage is that the array 302 may be selectively configured to meet the demands of specific test purposes and need not be provided with too many channels. Additional channels may be selectively added or removed to meet future demands.

[0044] The individual channels of the optical source array 302 are modularly constructed to meet the needs of specific test situations. By way of example, in the optical source array 302, a laser source module bank 304 includes a plurality of individual laser source module cards, e.g., card 306 including a laser diode or any other type of optical telecommunications laser source. An example of a commercially available laser source module is the 515 module available from ILX Lightwave of Boulder, Colo. A modulation switch circuitry bank 308, e.g., comprising individual switch circuitry 310, permits selective laser modulation according to permitted system modulation functions, such as sine wave, square wave, triangular or sawtooth wave, and rectangular wave function modulations, for each laser source module card. A thermal control bank 312 is formed of the previously described individual Peltier thermoelectric devices 314, as shown in FIGS. 1 and 2. These devices compensate for temperature variances in the individual laser diodes of the laser source module array 304 in providing a stable pulse modulated laser output. In each channel, the laser source module cards, such as card 306, preferably include the switch circuitry 310 and the thermoelectric devices 314 as integral components, however, selected portions of the switch circuitry 310 and the thermoelectric devices 314 may be provided as separate modular cards with compatible plug-in connectors. The thermoelectric devices heat or cool the laser diodes. The laser diode and system electronics are preferably mounted on a modular card. A plurality of such modular cards can be mounted adjacent to one another in a total number not less than twenty modular cards, e.g., to form an optical source array 302 comprising forty-eight, one-hundred or more adjacent cards. The modular cards forming the optical source array 302 are preferably identical to one another except that the laser diodes may emit light at different wavelengths.

[0045] A channel option array 316 comprising individual channel option cards, such as card 318, may be selectively added using commercially available components to provide shutter control for each laser, a variable optical attenuator, a polarization controller a polarization scrambler, a power monitor, or a wavelength reference. These devices may be used individually, selectively combined in series, or not used at all, depending upon test needs.

[0046] In cases where the channel option card 318 is a power monitor card, it is preferred to use a tap coupler, e.g., a 99%/1% coupler where power measurement is made on the 1% tap. Prior power monitor devices monitor current at a laser chip on the laser source card and use this measurement to stabilize the power output of the laser. Prior techniques are, therefore, only sensitive to laser effects that can affect power stability; however, these techniques are insensitive to power changes that derive from changes in the other optical and circuitry elements connected to the laser. Placing a power monitor downstream of the laser in the position of card 118 advantageously permits monitoring and/or selective adjustment of laser power output based upon the total channel laser power output.

[0047] Where, for example, the channel option card 318 is a polarization controller or polarization scrambler, the card operates upon polarized light from the laser source card 306 to align polarization in a controlled manner to optimize external modulation power and to control polarization dependent dispersion and polarization-dependent loss. A polarization scrambler generates all states of polarization in a certain time interval, which averages out polarization-dependent effects. By way of example, one commercially available device that can be used as both a polarization alignment device and a polarization scrambler is the model PCS-3X-PC/APC-7 available from General Photonics.

[0048] Where, for example, the channel option card 318 is a wavelength reference, or wavelength lock, an optical filter and power meter provide feedback that measure and stabilize the laser frequency from laser source card 306. The feedback signal is derived using the intensity or phase of light that is reflected from or transmitted to the filter.

[0049] Where, for example, the channel option card 318 is a shutter, the shutter mechanism, such as a mechanically actuated fiber switch in a V-groove mount, is preferably used to disrupt or transmit laser emissions from the laser source card 306 without having to change the current at the laser. This ability avoids the necessity of deenergizing and reenergizing the laser, which requires a long settling time to stabilize laser emissions upon reenergization. By way of example, commercially available shutter devices include model FOSW 1-1-L-PC-L-1 shutter from Lightwave Link, which has a 50 ms switching time.

[0050] Where, for example, the channel option card 318 is a variable optical attenuator, such as the OZ Optics model DD-100-11-1550-9/125-S-40-3D3S-1-0.5-485:1-6-MC/SPI, the attenuator is used to reduce the intensity of light in the channel 303 to much lower and stable power levels than the laser source card 306 can achieve alone with a reduction in current. The individual channel attenuator reduces the power level of the channel for whatever level is needed for the system under test by producing a combined comb using one device before the comb is delivered to a system under test.

[0051] Each channel in the optical source array 302 shares a common electrical/optical backplane 320 and a common electrical/optical backplane 322, which respectively provide compatible electrical or optical couplings that mate with corresponding couplings on the individual channels. The specific manner of connectivity is not critical, so long as the connectors provide the optical and electrical pathways that are required for module compatibility with optical test system 300.

[0052] An optional but preferred multiplexer (MUX) 324 combines the individual channel emissions from the optical source array 302 to provide a combined comb including the combined emissions. For example, a commercially available MUX is model AWG-NG48x1-100G-1.5-FC/APC from PIRI. The creation of a wavelength comb within a single instrument advantageously facilitates operations on the combined comb within the test system 300, as opposed to prior techniques requiring a separate device that occupies an additional footprint. Comb operations are, accordingly, simplified and expanded, as a single programmable controller is enabled to direct these functions in a more versatile manner than could be obtained from separate devices. An additional advantage is that fiber management and integrity is controlled within the enclosure of test system 300, reducing set-up time and the risk of fiber damage.

[0053] The optical pathway proceeds from the multplexer 324 to a series of optional modular service channel WDM processors 326 and 328, which are coupled with corresponding service channel sources 330 and 332 for conventional data transmission signal processing, e.g., for WDM-TDM handshake recognition relating to endpoint interpretation of the channels in the combined comb.

[0054] A beam splitter 334, e.g., a 99%/1% splitter, provides light from the combined comb to an auto-calibration device 336, which includes an optical filter and power meter that provide feedback for measurement and stabilization of the laser frequency. The feedback signal is derived using the intensity or phase of light that is reflected from or transmitted to the filter at emission wavelengths corresponding to the design wavelengths for the channels of laser source array 304. Power control of individual laser source cards in the laser source array 304 may, thus, be regulated after MUX processing to form a combined comb.

[0055] An optional variable optical attenuator 338, such as the OZ Optics model DD-100-11-1550-9/125-S-40-3D3S-1-0.5-485:1-6-MC/SPI, operates on the combined comb downstream of MUX 324 reduce the intensity of light in the combined comb to much lower and stable power levels than the laser source array 304 can achieve alone with a reduction in current. The individual channel attenuator reduces the power level of the channel for whatever level is needed for the system under test and operates on the combined comb using one device before the comb is delivered to a system under test.

[0056] A polarization controller or polarization scrambler 340 operates upon the combined comb downstream of MUX 324 to align polarization in a controlled manner to optimize external modulation power and to control polarization dependent dispersion and polarization-dependent loss. A polarization scrambler generates all states of polarization in a certain time interval, which averages out polarization-dependent effects and identifies minimum and maximum transmission orientations. By way of example, a commercially device that can be used as both a polarization alignment device and a polarization scrambler is model PCS-3X-PC/APC-7, which is available from General Photonics.

[0057] A splitter 342 divides the optical pathway for the combined comb into a polarized output segment leading to polarizer 344 and a non-polarized segment 346. The segment leading to polarizer 344 is in optical communication with an optical power measurement module 148, which monitors the power output in the combined comb at different polarization states. Optical connectors 350 and 352 are present to receive optical input from other sources external to the optical test system 300, such as a system power monitor 354 or a general-purpose power monitor 356.

[0058] The non-polarized segment 346 is advanced by a splitter 358 or a series of such splitters leading to an output panel 360 including a plurality of optical connectors 362 and 364. The panel 360 may be provided on the front or rear of the optical test system 300, or two or more such panels 360 may be present on both the front and rear or the sides.

[0059] The foregoing discussion has focused primarily upon the optical pathway within the optical test system 300, and the discussion of electronics has until now not included a discussion of the control circuitry. A master control circuit 366 preferably includes a central processing unit, magnetic or optical data storage, random access memory, and program logic, as required to interact with other system components of the optical test system 300 during normal system control operations in the intended environment of use. For example, master control circuit 366 may include a conventional motherboard for a personal computer, as well as any other circuitry and data storage devices that are commonly used with computers. Modulation control module 368 is provided to drive laser source emissions from the laser source array 306 according to system needs. The modulation control module 368 may also be incorporated as part of the master control circuit 366. The modulation control module 368 is provided with a plurality of N connectors, such as connector 370, for use in coupling with an external modulation input source 384. These connectors may be optical or electrical connectors, and the number N corresponds to the number N of channels in the optical source array 302. Thus, the external modulation input source 372 may be configured to drive modulation of the optical source array 302 in a manner that is not provided for by the electronics in the modulation control module 368.

[0060] The electronics on modulation control module 368 include a function generator that accepts instructions from the master control circuit 366 to drive individual elements (e.g., laser source card 306) of the laser source bank 304 in a predetermined manner that is compatible with test practices. This function generator may be switched to an OFF mode to accept external inputs. In an ON mode, the function generator provides sine waves, triangular or sawtooth waves, square waves, and any other wave form that is known or useful to those skilled in the art. The modulation depths are selectively adjustable from 0 to 100%. The modulation control module preferably provides signals with a plurality of these waveforms for availability to each channel in the optical source array 302, and individual channels are intelligent in the sense that they are programmed by instructions from the master control circuit 366 to accept one of the provided waveforms to energize the laser.

[0061] An optical or magnetic disk drive 374, such as a Zip drive, is used to provide software upgrades to master control circuit 366, as well as to log the performance of optical test system 300. These functions may also be accomplished using a modem or network connection to an appropriate server, e.g., an Internet server, or other suitable terminus.

[0062] A front panel display 378, e.g., a 10 inch color liquid crystal display or plasma display panel, provides a graphical user interface showing all of the source channels in the optical source array 302, their emission power levels, and the emission wavelengths. An intuitive command set is provided for interaction with the master control circuit 366 to allow rapid modifications to the system setup. Single source commands are provided to adjust the properties of individual lasers on each channel. Comb commands are provided to adjust the properties of the complete comb. Modulation functions are provided to adjust the operation of the modulation control module 368.

[0063] Optical test system 300 is compliant with any number of data transmission protocols that are commonly used in networking and optical test systems. External interfaces 378 exist for connections to other devices that use these protocols, such as RS-232, GPIB, and Ethernet. Furthermore, these interfaces preferably include a modem connection for either an internal or external modem, which interfaces with the manufacturer of optical test system 300 for trouble-shooting purposes. The modem may also provide real-time test measurement data summaries to remote locations or a telephony network.

[0064] Except for those components that are specifically noted above as being external to optical test system 300, all system components that have previously been described are preferably internal to a single box 380, and are provided as modular cards or boards that may easily be replaced or renewed on a component-by-component basis. This feature provides an extremely compact modular system that occupies a small volume footprint and can be upgraded for small incremental costs over a period of many years.

[0065] External optical and electrical systems can also be provided for use in combination with the optical test system 300. For example, each channel in optical source array 302 is preferably provided with an optical connector, such as connector 382, that accepts a fiber optic coupling for connection with an additional optical source system, such as external microwave modulation system 384, which may, for example, be an optical test mainframe. In this manner, additional sources may be combined into the comb that is processed through MUX 324.

[0066] Similarly, external optical devices may be provided downstream of the optical test system 300, e.g., a generic device 386, with power measurements being obtainable at any point from the downstream pathway by a simple tap, such as tap 388, for feedback to the optical power measurement module 348 through one of connectors 350 or 352. Further splitters, such as 2×2 splitter and 1×1 splitter 392 may be used as needed to branch the optical pathway to other equipment 394, which may include measurement systems such as power meters and the like, or it may branch to open system architecture or networks. Other pathway branches, for example, lead to test equipment, which may include 1×N switches for the testing of, for example, erbium doped fiber amplifiers (EDFA) or other DWDM system components.

[0067] Any of the components of optical test system 300 that have been previously described may benefit from the use of a thermoelectric device of the type shown in FIGS. 1 and 2 where the performance of the component would benefit from controlled heating and cooling.

[0068] According to still further aspects and instrumentalities of the thermoelectric control system and its preferred embodiments, there will now be shown a two-stage thermoelectric temperature control system for controlling the temperature of a laser diode. The system comprises a laser housing containing a laser diode device and a first switch-mode bi-directional thermoelectric cooler/heater disposed in the laser housing and heat-conductively connected to the laser diode device. The laser housing may be mounted on a heat-conducting mount, and a second switch-mode bi-directional thermoelectric cooler/heater can be mounted on the mount or in contact with the laser diode. Separate control circuitry may be adapted in the manner shown above to operate the first and second switch-mode bi-directional thermoelectric cooler/heater at different temperatures.

[0069]FIG. 4 and FIG. 5 depict a cross-sectional and a side elevational view, respectively, of an exemplary, general-purpose laser diode-mounting fixture 400 in which the relative locations and dimensions of thermoelectric cooler/heaters in accordance with the invention are shown. A wall 404 defines an inside space 406, an exterior space 407, an inside surface 408, and an opening 410. A mounting block 412 is disposed on the inside surface 408 covering opening 410. A plurality of switch-mode bi-directional thermoelectric devices 414 and 416, such as the Peltier junction thermoelectric devices 104 shown in FIG. 1, are operably coupled with appropriate control and drive circuitry for selective heating and cooling of the general purpose laser diode-mounting fixture 400. These thermoelectric devices 414 and 416 are attached to inside surface 408 above and below opening 410, respectively, between inside surface 408 and mounting block 412. Thereby, thermoelectric devices 414, 416 are heat-conductively connected to mounting plate 412, which typically comprises aluminum. A laser module plug connector 420 is provided in mounting plate 412 for coupling with a laser diode package. The laser module plug connector 420 is disposed substantially within inside space 406. A portion 422 of laser module plug connector 420 is disposed towards the exterior 407 and opening 410. A third switch-mode bi-directional thermoelectric cooler 424 in accordance with the invention is located within laser module 420 where it actively heats and cools the laser diode module 420. The outer surface of wall 404 forms a plurality of heat-dissipative fins 426 having an increased surface area for communicating heat energy between the wall 404 and the environment of use.

[0070]FIG. 6 depicts an alternative laser diode mounting system 600. A thermoelectric device 602 is preferably a Peltier junction device of the type shown as thermoelectric device 104 in FIG. 1. An aluminum heat-conducting block 604 is positioned between the thermoelectric device 602 and a laser diode package 606. The thermoelectric device 602 is in direct contact with an aluminum heat conductive plate 608. The thermoelectric device 602 and the aluminum heat conductor 604 preferably have hollow interiors to accommodate electrical conductors for the proper operation of the laser diode package 606 and mounting system 600.

[0071]FIG. 7 provides additional detail with respect to the laser diode package 606 shown in FIG. 6. A thermoelectric device 700 is preferably a Peltier junction device of the type shown as thermoelectric device 104 in FIG. 1. The thermoelectric device 700 is in direct contact with a heat sink 706 and a laser diode 704. A heat shield 708 is provided to shield adjacent devices from radiant heat effects.

[0072]FIG. 8 is a circuit diagram showing a particularly preferred capacitive filter 800 that may be interposed on line 21 between the switch-mode power supply 200 and the H-bridge 214 (see also FIG. 2). The capacitive filter 800 comprises, in series, and inductor 802 and a capacitor 804. The capacitor 804 may be connected to ground 806 or, alternatively, a voltage that enhances the capacitive effects of the capacitor 804.

[0073]FIG. 9 depicts the intended result of the capacitive filter 800 where the pulse mode power supply 216 (see FIG. 8) produces a series of pulses, such as pulses 900 and 902. The capacitive filter 800 operates upon these pulses by averaging them to form a smoothed filter output curve 904thatis preferably a continuous curve that is essentially steady-state over an interval of time. The integral controller 208 (see FIG. 2) may cause the switch-mode power supply 220 to vary the amplitude and/or width of these pulses to either raise or lower the power magnitude of curve 904.

[0074] The preceding discussion is intended to illustrate various embodiments of the invention by way of example, and not by way of limitation. For example, although the above discussion emphasizes the importance of heating and cooling laser diodes, it is also understood that any number of high performance electronic systems may also benefit from heating and cooling through the use of a bi-directional Peltier junction. Furthermore, the associated circuitry that is described above may be replaced by functionally equivalent circuitry without departing from the broad principles of the invention. Accordingly, the inventors hereby state their intention to rely upon the Doctrine of Equivalents, in order to protect their full rights in the invention. 

1. A system for heating and cooling an object, comprising: a first thermoelectric cooler/heater having a Peltier junction between a first contact and a second contact; a switch-mode power supply electrically connected to the first contact and the second contact, configured for flowing electrical current through the Peltier junction; and a polarity controller configured for controlling the direction of electrical current flow through the Peltier junction.
 2. The system as set forth in claim 1, wherein the switch-mode power supply is configured to provide DC current.
 3. The system as set forth in claim 1, wherein the switch mode power supply is configured to provide pulse-modulated current.
 4. The system as set forth in claim 3, including a filter for use in smoothing the pulse-modulated current.
 5. The system as set forth in claim 4, wherein the filter is a capacitive filter.
 6. The system as set forth in claim 5, wherein the capacitive filter comprises an inductor preceding a capacitor.
 7. The system as set forth in claim 1, wherein the object comprises a laser diode contacting the first thermoelectric cooler/heater.
 8. The system as set forth in claim 7, comprising a heat conductive block contacting the first thermoelectric cooler/heater, and a second thermoelectric cooler/heater contacting the heat conductive block.
 9. The system as set forth in claim 8, including control circuitry operable to maintain each of the first and second thermoelectric cooler/heaters at different temperatures during system operation.
 10. The system as set forth in claim 1, comprising a closed loop feedback system including a temperature sensor contacting the object and configured to provide an input signal useful for controlling system temperature.
 11. The system as set forth in claim 10, wherein the temperature sensor comprises a thermistor and the input signal comprises a thermistor voltage signal.
 12. The system as set forth in claim 11, including an error amplifier that operates by comparing the thermistor voltage signal against a reference voltage representing a desired control temperature.
 13. The system as set forth in claim 12, comprising a digital to analog converter configured to provide the reference voltage.
 14. The system as set forth in claim 1, wherein the control circuitry includes a thermal process controller adapted to operate on a temperature signal.
 15. The system as set forth in claim 14, wherein the thermal process controller comprises a PID controller.
 16. The system as set forth in claim 14, wherein the thermal process controller comprises a PI controller.
 17. The system as set forth in claim 1, including a polarity control bridge adapted to electrically activate the thermoelectric cooler/heater based upon output from the polarity controller.
 18. The system as set forth in claim 17, wherein the polarity control bridge comprises an H-bridge.
 19. The system as set forth in claim 1, wherein the control circuitry includes a thermistor, an error amplifier, a thermal process controller, and a polarity control bridge forming a first loop.
 20. The system as set forth in claim 19, wherein the switch-mode power supply is connected to the polarity control bridge for supply of power thereto.
 21. The system as set forth in claim 20, comprising an absolute value circuit positioned between the thermal process controller and the switch-mode power supply to form a second loop which is a subset of the first loop.
 22. The system as set forth in claim 21, comprising a third loop including means for providing feedback based upon output of the switch-mode power supply, the third loop being operable to adjust the output of the switch mode power supply according to output from the thermal process controller.
 23. The system as set forth in claim 1 including process control circuitry configured to adjust power output of the switch-mode power supply based upon a first input signal from a first feedback loop.
 24. The system as set forth in claim 23, wherein the first feedback loop is a temperature feedback loop and the input signal is a voltage signal based upon a temperature of the object.
 25. The system as set forth in claim 1, wherein the process control circuitry is configured to adjust power output of the switch-mode power supply based upon a second input signal from a second feedback loop.
 26. The system as set forth in claim 25, wherein the second feedback loop operates by comparing actual output and intended output of the switch-mode power supply, and by adjusting power output of the switch-mode power supply to meet the intended output.
 27. The system as set forth in claim 1, comprising a laser diode as the object, the laser diode and system being mounted on a modular card, and a plurality of such modular cards mounted adjacent to one another in a total number not less than twenty modular cards, the modular cards being identical to one another except that the laser diodes may emit light at different wavelengths.
 28. A system for heating and cooling an object, comprising: a thermoelectric cooler/heater having a Peltier junction between a first junction contact and a second junction contact; a switch-mode power supply electrically connected to the first junction contact and the second junction contact, for flowing electrical current through the thermoelectric cooler/heater through the Peltier junction; a thermistor for converting a temperature of the object to a thermistor voltage; an error amplifier for comparing the thermistor voltage to a reference voltage and producing an error voltage; a PID controller for processing the error voltage and producing a PID signal; an absolute value circuit for converting the PID signal to a negative feedback value for input to the switch-mode power supply; an H-bridge for reversing the direction of current through the Peltier junction; a polarity controller for sensing the polarity of the PID signal and controlling the H-bridge; and a current-voltage amplifier for converting the electrical current that flows through the thermoelectric cooler/heater into a feedback signal for use in controlling the output of the switch mode power supply.
 29. A two-stage thermoelectric temperature control system for controlling the temperature of a laser diode, comprising: a laser housing containing a laser diode device; and a first switch-mode bi-directional thermoelectric cooler/heater disposed in contact with the laser housing and heat-conductively connected to the laser diode device.
 30. The two-stage thermoelectric temperature control system as set forth in claim 29, comprising: a heat-conducting mount on which the laser housing is mounted; and a second switch-mode bi-directional thermoelectric cooler/heater mounted on the mount.
 31. A thermoelectrically controlled high-density laser source bank, comprising: a plurality of laser diode source modules, each laser diode source module containing a laser diode and a switch-mode bi-directional thermoelectric cooler/heater having a Peltier junction.
 32. The thermoelectrically controlled high-density laser source bank as set forth in claim 31, wherein each laser diode source module includes: a laser housing containing a laser diode device; a first switch-mode bi-directional thermoelectric cooler/heater disposed in contact with the laser housing and heat-conductively connected to the laser diode device; a heat-conducting mounting block, on which the laser housing is mounted; and a second switch-mode bi-directional thermoelectric cooler/heater mounted on the mounting block.
 33. A method of stabilizing temperature in a system having a first Peltier junction thermoelectric cooler/heater, the method comprising the steps of: sensing the temperature in the system to provide a temperature signal corresponding to the temperature; and selectively activating the first Peltier junction thermoelectric cooler/heater for heating and cooling purposes to maintain the temperature within a predetermined temperature range based upon the temperature signal, wherein the step of selectively activating the first Peltier junction thermoelectric cooler/heater includes utilizing a switch-mode power supply.
 34. The method according to claim 33, wherein the system includes a laser diode and the step of sensing the temperature includes sensing the temperature of the laser diode.
 35. The method according to claim 34, including a step of performing optical telecommunications test operations by energizing the laser diode concomitantly with the steps of sensing temperature and selectively activating the first Peltier junction thermoelectric cooler/heater.
 36. The method according to claim 34, wherein the system includes a heat sink contacting the laser diode and an additional thermoelectric heater/cooler, the method comprising an additional step of selectively activating an additional Peltier junction thermoelectric cooler/heater.
 37. The method according to claim 36, wherein the additional step of selectively activating the additional Peltier junction thermoelectric cooler/heater includes maintaining the first Peltier junction thermoelectric cooler/heater and the additional Peltier junction thermoelectric cooler/heater at different temperatures.
 38. The method according to claim 34, wherein the step of sensing temperature comprises sensing temperature from a structure selected from the group consisting of a laser diode and a laser diode module.
 39. The method according to claim 34, wherein the step of sensing temperature comprises using a thermistor to provide the temperature signal.
 40. The method according to claim 34, wherein the system includes a thermistor for converting a temperature of the object to a thermistor voltage, and the step of sensing the temperature comprises using the thermistor to provide the temperature signal.
 41. The method according to claim 40, wherein the system includes an error amplifier, and the method includes a step of comparing the temperature signal to a reference signal to produce an error output signal.
 42. The method according to claim 41, wherein the step of selectively activating the Peltier junction thermoelectric cooler/heater comprises integrating the error output signal to provide and integrated value and providing control signals for use in heating and cooling operations based upon the integrated value.
 43. The method according to claim 34, wherein the step of selectively activating the Peltier junction thermoelectric cooler/heater comprises converting the integrated value into an absolute value for use as control input to a switch mode power supply.
 44. The method according to claim 34, wherein the step of selectively activating the Peltier junction thermoelectric cooler/heater comprises adjusting output of the switch mode power supply based upon a feedback comparison between desired output and actual output.
 45. The method according to claim 45, wherein the step of selectively activating the Peltier junction thermoelectric cooler/heater comprises adjusting output of the switch mode power supply based upon a feedback comparison between actual and desired temperature of the object. 